1. Field of the Invention
The present invention relates to a monitor for determining the concentration of sulfate (SO.sub.4) in a fluid sample stream, and more particularly, a continuous on-line differential conductivity monitor for measuring trace sulfate impurities.
2. Description of the Related Art
Sulfate is one of the most common contaminants in the steam cycle water of fossil and nuclear fueled power generating plants. Sources of sulfate in steam cycle water are condenser inleakage, ion exchange resin ingress, and improper regeneration of condensate polishers with sulfuric acid. Non-volatile impurities, particularly sulfate, concentrate quickly on turbine blades and in "dry-out" regions of a boiler or steam generator. The concentrated impurities can lead to accelerated corrosion and/or a loss in operating efficiency. Thus, there is a need to monitor the sulfate concentration of steam cycle water.
Sulfate (sulfuric acid) is one of the main components of acid precipitation (acid rain) and is present as a consequence of the burning of sulfur containing fossil fuels. Damage to the environment from acid rain has been well documented, but is not completely understood. The ability to continuously monitor natural waters affected by acid rain for sulfate will further the understanding of the problems associated with acid rain and facilitate regulation of acid rain pollution.
The various techniques for monitoring sulfate are as follows:
Cation conductivity, the electrical conductivity of a fluid sample that has been passed through a cation exchange column in the H.sup.+ form, is a sensitive method for continuously monitoring anionic impurities. Cation conductivity measurements, however, do not determine the concentration of individual impurities or contaminants in a fluid sample.
Ion chromatography is a sensitive and specific technique for sulfate monitoring, but, ion chromatographs are, by their nature, non-continuous monitors. Further, the hardware required for ion chromatography is both complex and expensive.
The methylthymol blue flow injection method is sensitive in a range of 100 ppb to 6000 ppb. This measurement range may be satisfactory for some acid rain measurements, but it does not provide monitoring in the 0-100 ppb range necessary to monitor sulfate in the steam cycle water of a power generating plant.
U.S. Pat. No. 4,251,219, Larson et at., discloses an apparatus for monitoring the purity of condensate in boiler systems, such as steam power plants and pressurized water reactor nuclear systems. The apparatus passes condensate through a hydrogen exchange resin bed and heats the effluent from the resin bed to the atmospheric boiling point temperature. The conductivity of the heated effluent is measured at or close to the atmospheric boiling point temperature and is an indication of the concentrations of chloride, sulfate, phosphate, nitrate, and other inorganic anions, in relatively low pressure condensate. This apparatus, however, relies on a conductivity measurement which does not determine the concentration of the individual impurities or contaminants.